1. Field of the Invention
The field of the present invention is cooling systems using a coolant for multi-cylinder engines.
2. Description of the Prior Art
Conventional cooling systems typically have a common coolant jacket around a plurality of cylinder bores in a cylinder block of a multi-cylinder engine. Cooling water flows through the coolant jacket to cool the periphery of the cylinder bores.
In these known cooling systems, however, certain problems are encountered. The cylinder bores are surrounded, over a region from their upper portions to their lower portions, by a common coolant jacket. Hence, a cylinder located away from a coolant inlet may be cooled by coolant which has already been warmed by another cylinder located near the inlet. Thus, the cylinders tend to be cooled unevenly. In addition, due to a variation and unevenness in the flow area of the coolant passages, not only may the flow resistance of the coolant passages be increased, but also the coolant may be apt to stagnate at certain locations. Consequently, the total cooling efficiency suffers.
In addition, certain systems involve a cylinder liner having an outward flange at its upper end, inserted into the cylinders. With these systems, it is difficult to uniformly and efficiently cool the flange portion of the cylinder liner, which is heated to a relatively high temperature. Particularly, in a cooling system in which the spacing between cylinders is reduced in order to make the engine compact, adjoining portions of the flanges of the adjacent cylinder liners are chamfered and placed in contact with each other. Then, in the prior art, it has been impossible to directly cool such contacting portions of the flanges.
Another multi-cylinder engine has an engine block including a cylinder block having a block-side coolant jacket surrounding cylinder bores and a cylinder head having a head-side coolant jacket coupled to the block. The head-side coolant jacket surrounds the combustion chambers defined above the pistons and communicates with the block-side coolant jacket. Opposite outside walls of the cylinder head extend parallel to the crank shaft and are substantially aligned with opposite outside walls of the cylinder block (for example, see Japanese Patent Application Laid-open No.81451/85). In such multi-cylinder engines, the head-side coolant jacket is provided over substantially the entire surface of the cylinder head. In some cases, the cylinder block may have an outside wall spaced outwardly from the block-side coolant jacket, in order to improve the rigidity and strength of the cylinder block. In such cases, if the head-side coolant jacket is provided over substantially the entire surface of the cylinder head as described above, coolant flows over a wide area, including portions other than the combustion chamber area of the cylinder head, where the highest temperatures occur. Consequently, the flow speed of the coolant within the head-side coolant jacket is reduced, resulting in a decreased cooling efficiency in the cylinder head.